Get line that contains and then get the second and fourth line after that.

Question

So I have a text file and I want it to find all the lines in the file that contain an @ symbol and then I want it to get that line and the line second and fourth from that line. Then I would export it like this:
$linewith@ + ":" + $secondline + ":" + $fourthline
Finding the lines with an @ symbol is easy, but how would I tell it to get the second and fourth line after the line with an @ symbol?
So I would get the lines with something like this:
foreach ($line in [System.IO.File]::ReadLines($filename)) {
if($line.contains("@")){}

Answer 1

That worked perfectly thanks man! Here is the entire code. I'm sure it could been cleaned up. I'm still learning powershell. 
$username = "Username"
$password = "Password"
$url = "http://URL"
$ie = New-Object -com InternetExplorer.Application
$ie.visible=$false
$ie.navigate($url)
while($ie.ReadyState -ne 4) {start-sleep -m 100}
$ie.document.getElementById("username").value = "$username"
$ie.document.getElementById("password").value = "$password"
$ie.document.getElementById("click").click()
start-sleep 20
$ie.Document.body.innertext | Out-File -FilePath c:\web.txt
$links = $ie.Document.getElementsByTagName('A')
$logout = $links | where {$_.innerText -eq 'logout'}
$logout.click()
start-sleep 5
(gc C:\web.txt) | ? {$_.trim() -ne ""} | set-content C:\web.txt
( Get-Content C:\web.txt | Select-Object -Skip 2 | ForEach-Object { $_.TrimStart( " " ) } ) | Set-Content C:\web.txt
start-sleep 5
$fileContents = Get-Content C:\web.txt
foreach ($line in $fileContents) {
if ($line -like '*@*') {
$line + ":" + $($fileContents[$line.ReadCount+0]) + ":" + $($fileContents[$line.ReadCount+3]) | Out-File -FilePath c:\finish.txt -Append